Collective immunity is “mythical” with the delta variant of Covid, according to experts

LONDON – Achieving herd immunity with Covid-19 vaccines when the highly infectious delta variant spreads is “not a possibility,” a leading epidemiologist said, experts agreeing that such a goal – where the Overall immunity in a population is reached and the spread of the virus is stopped – is unlikely for several reasons.

Professor Andrew Pollard, head of the Oxford Vaccine Group, told UK lawmakers on Tuesday that as Covid vaccines did not completely stop the spread of the virus – vaccinated people could still be infected and transmit the virus – the idea to achieve collective immunity was “mythical.”

“I think we’re in a situation here with this current variant (the delta variant) where herd immunity is not a possibility because it always infects vaccinated individuals,” Pollard, one of the lead researchers in the creation. of the AstraZeneca-University of Oxford vaccine, says.

“And that means anyone who is still not vaccinated, at some point, will encounter the virus. It might not be this month or next month, it could be next year, but at some point, they will meet the virus and we don’t have something that will stop this transmission. “

Read more: Fully vaccinated people are still infected with Covid. Experts explain why

Simply put, herd immunity is related to the idea that a high level of immunity against a virus in a population can be achieved both through natural infection (through the formation of antibodies when the body fights a virus) and vaccination.

The latter method is preferred because vaccines massively create immunity without causing disease or adverse health complications, unlike the natural route of infection.

Antibodies provided by both natural infection and vaccination generally protect against future infection, and if enough people in a population are immunized, this leads to lower disease or virus prevalence rates in a community. If a virus is less likely to spread and infect, it can be significantly controlled or even eradicated.

With herd immunity, those who are not vaccinated (whether by choice or because they cannot be immunized at some point – newborns, for example) are protected by the overall level of immunity. present in a population.

Massive and successful vaccination programs have meant that deadly and contagious viruses and diseases such as polio, tuberculosis and measles have been largely eradicated in some parts of the world or largely suppressed by vaccination programs and immunity collective that they promote.

Pollard noted on Tuesday that Covid, and the current virulent delta variant, were different. “The problem with this virus is [it is] not measles. If 95% of people have been vaccinated against measles, the virus cannot be transmitted in the population, “he told the British parliamentary group on the coronavirus.

Pollard said that while Covid vaccines could slow the spread of the virus – because fully vaccinated but infected people appeared, in studies, to shed fewer viruses, giving the virus less chance of spreading – new variants were likely to ’emerge that would also spread.

“I suspect that what the virus will vomit next is a variant that is perhaps even better to transmit among vaccinated populations and so this is even more of a reason not to create a vaccination program around herd immunity. . “

People fully vaccinated against Covid-19 are highly protected against serious infections, hospitalizations and death caused by the virus. New research from the UK released last Friday also showed that double-vaccinated people were three times less likely than unvaccinated people to test positive for the coronavirus. The research, led by Imperial College London, also suggested that fully vaccinated people may be less likely than unvaccinated people to pass the virus on to others.

Experts are calling on all unvaccinated people to come forward, but problems are emerging in some countries in Europe and the United States with young adults not taking the vaccine.

Andrew Freedman, infectious disease reader at Cardiff Medical School, told CNBC on Thursday that he agreed with Pollard’s diagnosis that herd immunity was an unlikely prospect.

“The delta variant is highly transmissible, which means that the proportion of people who need to be fully vaccinated for herd immunity is probably not achievable,” he noted. “The vaccines offer very effective protection against serious illness / hospitalization / death, but are less effective at preventing infections, mild illness and transmission, especially for the delta variant.”

In countries like the UK, herd immunity was also unlikely due to the large number of unvaccinated adolescents and children – some of whom are said to be immune as a result of natural infection, but most do not. would not, Freedman noted.

“However, even without full ‘herd immunity’, the higher the proportion of the population that is fully immunized, the lower the incidence of infection in the community,” he said.

When the coronavirus pandemic began to spread around the world in 2020, a number of governments, like those in Sweden and the United Kingdom, seemed ready to place their hopes in the concept of “herd immunity”, ready to let the virus spread among their populations so that natural immunity can develop.

However, the approach was quickly abandoned by the UK, as it quickly became evident how deadly and destructive Covid could be, with thousands of infections leading to hospitalizations and deaths threatening to overwhelm the system. health.

Achieving collective immunity with respect to Covid is considered much more difficult for a number of other reasons, including uneven vaccine deployments, vaccine hesitation, and virus mutation, with new variants threatening (but not yet undermining) the effectiveness of the Covid vaccine.

Read more: As Covid mutations spread, will collective immunity ever be possible?

Additionally, experts do not yet know how long immunity to Covid lasts, although there is clinical evidence that immunity against the virus (whether immunity is naturally acquired through infection or vaccination) decreases with increasing frequency. time.

Studies show that the Covid vaccines used in Europe and the United States are still very effective in preventing serious infections, hospitalizations and deaths. While there is evidence of so-called “breakthrough” Covid cases among fully vaccinated people, these cases are very rare and tend to be milder.

Danny Altman, professor of immunology at Imperial College London, told CNBC that he also agrees with Pollard and that the mathematical model of herd immunity cannot be easily applied to a virus “without precedent “like Covid which was still little understood with discrepancies, circulating in the world emerging variants.

“The collective immunity package was one of those pieces of medical textbooks that were adopted early on by political advisers, then the press, then the public and were distorted and simplified all the time at the extreme, ”he said Thursday.

What was important, said Altmann, was that “the more people around the world are effectively vaccinated, the fewer copies of the virus we will have on the planet, so less the spread and fewer lungs in which the virus mutates and spreads the virus. next wave of variations. “